Illusionist has some spectators hold a piece of newspaper or similar paper up to a window.
He knocks on it to show it's very solid, and so does some audience members.
He askes everyone to step back, and goes behind the window, then goes THROUGH the paper, thus THROUGH the window!!!!
David Blaine popularised this illusion by grabbing a watch through a window, and Criss Angel did this in an episode of Mindfreak. There is even a similar version called Devil's Reflection on sale on the internet.
